1. Field of the Invention
The present invention relates to a data processing method, a data processing apparatus, a printer, a communications protocol, a storage medium, etc. for performing a data communicating process.
2. Related Background Art
When communications are established through one-to-one connection between a host and a device in various interfaces such as Centronics, USB, IEEE 1394, etc., the communications are performed by setting a plurality of logical communications units in a session of a communications protocol, that is, a logical channel connection, to control various functions of devices between a host and a device.
These logical channels are flow-controlled (communications control) for each channel. Normally, when a plurality of logical channels are used, there can be a configuration in which two types of logical channels, that is, a channel from the host to the device and a channel from the device to the host according to a data transfer direction, are provided, a configuration in which a plurality of bidirectional logical channels are provided for each control function, etc.
However, when data cannot be transmitted/received through a logical channel for any reason, a control command itself for getting the transmission/reception back to normal cannot be transmitted to the logical channel. If the data transfer of a channel from the host to the device cannot be smoothly performed when a one-way data channel is provided for each data transfer direction, then it is obvious that command data cannot be transmitted from the host to the device through the channel. Furthermore, when flow control is not smoothly performed in a channel unit with a bidirectional logical channel provided for each control function, the command cannot be transmitted through the channel.